Field of the Disclosure
The present disclosure relates to a non-reciprocal circuit element, and particularly relates to a non-reciprocal circuit element such as an isolator or a circulator used in the microwave bands or other bands.
Description of the Related Art
In general, a non-reciprocal circuit element such as an isolator or a circulator has characteristics of transmitting signals only in a specific direction and not transmitting signals in the opposite direction, and is mounted in a transmitting circuit unit of a mobile communication apparatus such as a cellular phone.
Patent Document 1 describes a two-terminal-pair isolator in which first and second center conductors are disposed near the center of a ferrite, to which a static magnetic field is applied, so as to intersect each other in an electrically insulated state, ends of the first and second center conductors are first and second input/output terminals, respectively, the other ends of the first and second center conductors are connected to ground, a first matching capacitor is connected between the first input/output terminal and the ground, a second matching capacitor is connected between the second input/output terminal and the ground, a resistance element is connected to the first and second input/output terminals, and the intersection angle between the central axis of the first center conductor and the central axis of the second center conductor is 40° to 80°.
Patent Document 2 describes a two-port-type isolator in which a first center electrode and a second center electrode are disposed on a ferrite, to which a DC magnetic field is applied, so as to intersect each other in an insulated state, one end of the first center electrode is connected to an input port, the other end of the first center electrode and one end of the second center electrode are connected to an output port, the other end of the second center electrode is connected to a ground port, and further a matching capacitor and a resistance element are connected in parallel between the input port and the output port.
Patent Document 3 describes a magnetic resonance (ferrite absorption) isolator that includes a ferrite, a junction conductor disposed on the ferrite and having a first port, a second port, and a third port, and a permanent magnet for applying a DC magnetic field to the ferrite, and in which a main line disposed between the first port and the second port of the junction conductor does not resonate, an end portion of a sub-line branching from the main line is the third port, a reactance element is connected to the third port, the reactance element is connected to ground, and an impedance matching circuit is connected to the first port and the second port.
Non Patent Document 1 describes a circulator in which center electrodes are overlaid on a ferrite, to which a DC magnetic field is applied, so as to intersect each other at an angle of 120° in an electrically insulated state.
Non Patent Document 2 indicates that it is possible to improve electric power resistance by substituting a garnet ferrite (YIG) with Co, Ho, and Dy.
Meanwhile, in recent years, a non-reciprocal circuit element has been reduced in size, and the lengthwise and crosswise dimensions are 2.0 mm and the thickness dimension is 0.60 mm or less so that the size of the non-reciprocal circuit element is very small. Thus, when such a non-reciprocal circuit element is used in a wireless apparatus, there have been apparent needs to improve the electric power handling capability and to reduce the leakage power between the adjacent channels. In addition, in a non-reciprocal circuit element, it is desirable to reduce the noise between the adjacent ports. However, when an attempt is made to reduce the noise, a problem of an increase in the insertion loss arises, and thus it is also necessary to take a balance therebetween.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2003-046307
Patent Document 2: International Publication No. 2007/046229
Patent Document 3: International Publication No. 2011/077803
Non Patent Document 1: Systematization of Ferrite Technology, Systematization Investigation of Technology of National Museum of Nature and Science, Vol. 13, 2009, p 171
Non Patent Document 2: Microwave Ferrite and its Applied Technology, p 161, written by Tadashi Hashimoto